In recent years, for efficiently utilizing a limited frequency band, radio communication systems have been using multiple-antenna techniques with which at least one of a transmission side and a reception side uses multiple antennas. One of known multiple-antenna techniques is for multiple-input multiple-output (MIMO) communications in which multiple signal sequences using the same frequency are simultaneously transmitted via multiple transmission antennas and then received via multiple reception antennas, and then, the received signal sequences are demultiplexed from each other.
The MIMO communications include a scheme in which the reception side estimates propagation channel characteristics between the reception side and the transmission side and then feeds back feedback information based on the estimated propagation channel characteristics to the transmission side (so called, closed loop MIMO). The transmission side performs various types of transmission control, e.g., weighting on each of the transmission antennas. With the closed loop MIMO, the communication quality can be improved because the transmission side can perform transmission control adapted to a change in the propagation channel characteristics.